Antioxidant defence-related genetic variants are not associated with higher risk of secondary thyroid carcinoma after treatment for childhood cancer
Background. Secondary thyroid carcinoma is one of the most common neoplasms after childhood cancer treatment. Thyroid gland is very sensitive to the carcinogenic effect of ionizing radiation, especially in children. Imbalance between pro- and anti-oxidant factors may play a role in thyroid carcinogenesis. Our study aimed to assess the relationship between genetic variability of antioxidant defence-related genes and the risk of secondary thyroid cancer after treatment for childhood cancer.
Patients and methods. In a retrospective study, patients with secondary thyroid cancer (cases) and controls matched for age, gender, and primary diagnosis were genotyped for SOD2 p.Ala16Val, CAT c.-262C>T, GPX1 p.Pro200Leu, GSTP1 p.Ile105Val, GSTP1 p.Ala114Val and GSTM1 and GSTT1 deletions. The influence of polymorphisms on occurrence of secondary cancer was examined by McNemar test and Cox proportional hazards model.
Results. Between 1960 and 2006 a total of 2641 patients were diagnosed with primary cancer before the age of 21 years in Slovenia. Among them 155 developed a secondary neoplasm, 28 of which were secondary thyroid carcinomas. No significant differences in the genotype frequency distribution were observed between cases and controls. Additionally we observed no significant influence of investigated polymorphisms on time to the development of secondary thyroid cancer.
Conclusion. We observed no association of polymorphisms in antioxidant genes with the risk for secondary thyroid carcinoma after treatment for childhood cancer. However, secondary thyroid carcinoma is one of the most common secondary cancers after treatment for childhood cancer and the lifelong follow up of patients with childhood cancer is of utmost importance.